The human spine is particularly important because it protects the spinal cord, which is responsible for relaying electrical impulses from the brain to the rest of the body. Occasionally, an accident or other outside force may cause the vertebrae which make up the spine to be broken, cracked, or chipped. Each of these situations are dangerous, and are handled by the most skilled physicians and surgeons. The remedy for a broken, cracked, or chipped bone may be different for every individual, and may change according to the situation under which the injury occurred.
One situation that commonly arises occurs is when vertebrae or portions of vertebrae or spine are broken, cracked, or are beginning to fail to function normally. One treatment technique used by doctors to remedy this situation involves using a pair of rods that are connected to several vertebrae. The rods may be aligned along the periphery of the vertebrae, and are typically used to maintain the alignment of the bones. This may allow the vertebrae to re-grow bony tissue or cartilage. In addition, aligning the vertebrae allows them to heal properly, and prevents movement of the spine from injuring the spinal cord.
In order to prevent the movement of the spine, a fixation system is often used to hold the two rods together. The fixation system allows the rods to be fixed in place under normal conditions. Many fixation devices are currently available. They vary in shape, size, and their approach to preventing the rods from moving. One type of device that has been used involves a single connection body that lies in between the two rods, over the body of the vertebrae. Though this device serves the purpose of preventing the rods from moving, it also has several disadvantages. For example, many of these devices are unable to move, rendering them unable to adapt to the contour of the spine. Another limitation of these devices is that they typically do not allow for clearance of the body of the vertebrae, which can cause damage to the vertebrae or cause the device to protrude from underneath a person's skin.
Many devices hold the rods in place by gripping them from the outer portion of the bars. These devices also achieve the purpose of holding the bars in place, but have several limitations. For instance, these devices often may not be capable of achieving the same degree of grip on the rods as compared to a configuration that grips the bars from the inner area, between the bars.
Other devices have aimed to eliminate the limitations of their predecessors by providing two connecting bodies that have a small degree of adjustability. However, many of these devices are unable to translate axially, which prevents them from adjusting to the spacing between the rods. Other devices are unable to rotate to adjust for rods that aren't coplanar. Additionally, these devices often do not have the ability to rotate freely, preventing them from adjusting to the contours of the spine. Devices such as these may provide greater adjustability at the expense of increased complexity, number of components, increased overall height, or other limitations and disadvantages.
A continuing need exists for a spinal fixation system that is able to adjust the contours of the spine, is simple to install and meets the demanding mechanical loads that are experienced when implanted in a patient.